Not enough new orders placed to keep production lines open.If you want to keep a certain production line open then you need to place sufficient orders to keep it open when the "Production of Model XXX to Close' warning comes out

It seems that in your case the Production line may have been already closed when the GameWorld stared (or soon after), which would have been available on the New aircraft page to check.

the problem is the game time is too fast to get them. When i was in the position to place orders for new planes they were going out. So i think that closing time needs to be reconsidered for the pace of the game.

I now have 3 787-3 that i cannot extend on and had to switch to 350 that are still produced. The problem for me is canceling them is a little steep in pricing so i have now 4 fleetgroups that i did not intent to have.

(i got the 787 from the used market before) i couldnt grab more because again they got scraped (what a shame for that plane with an age of 2....)

Even with 20 minute days, you get 60 RL hours between the announcement that a production line might close, and the announcement that it is closed. 2.5 days is plenty of time to order planes if you want them.

I suspect what was more of a problem is that the 6 month countdown started less than 18 months into the game, and the planes are very expensive, so those who ended up wanting to get them hadn't planned ahead in time, and simply didn't have the cash to order enough planes.

As for cancelling your existing leases being a little steep, how long did you originally lease them for? The discount for very long leases, especially from the used market, is almost never worth the loss of flexibility.